Bump guage reality

Bucklowery

Well-Known Member
Joined
Jul 1, 2013
Messages
389
Location
northwest florida
Got a bump guage when I ordered some new locking nuts for dies. I started checking and resetting dies for shoulder bump on a couple that I load for long range. Is it that normal for factory chambers to be smaller normally. I found two to be smaller than Samii spec and new brass as well
The new brass did not surprise me so much as the chamber of the rifle. Do the readers wear that much and create the variance in mass production. I have always full length resized and set dies up according to directions and produced great ammo. Now that I am checking bump I am amazed. The ignorant bliss is over

Thanks

Buck
 

243winxb

Well-Known Member
Joined
Sep 9, 2016
Messages
492
Location
USA
Its good to use a bump gauge,, but fired brass doesn't always expand fully to a chamber. False measurement.

Bump gage/comparator is to compare fired & sized brass.Tolerances, see https://saami.org/

These measure chambers.
Go Gauge: Go Gauges match the minimum chamber dimensions allowable under SAAMI specifications. In order to accept SAAMI maximum ammunition, the rifle must be able to chamber the correct go gauge.



No-Go Gauge: No-Go Gauges are sized to the maximum recommended headspace dimensions. If a rifle will chamber the no-go gauge, it may still be within specifications, or this could indicate excessive headspace. To determine if the rifle is safe to shoot, the chamber must be checked with the field gauge.



Field Gauge: Field Gauges correspond to the maximum safe headspace dimension. If a rifle will chamber a field gauge, it should be inspected and repaired by a competent gunsmith prior to use.
Screenshot_20201025-161633_Chrome.jpg

Head clearance runs from .000" to .015" (Tolerances)
HEAD CLEARANCE
The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace
 
Last edited:

Bucklowery

Well-Known Member
Joined
Jul 1, 2013
Messages
389
Location
northwest florida
I think I expected to find the bump measurement for brass fired multiple times to be closer to the SAAMI headspace minimum. I know there has to be space for easy extraction. I am always learning and actually measuring has turned out to be just that. I appreciate your responses. I always set my new barrels for as tight a headspace as possible. I still have a couple factory gun that shoot very well

Thanks
Buck
 

YZ-80

Well-Known Member
Joined
Feb 20, 2019
Messages
1,145
Location
Maryland
I have always full length resized and set dies up according to directions and produced great ammo. Now that I am checking bump I am amazed. The ignorant bliss is over

Thanks

Buck

I can relate. If you follow the RCBS set up instructions you'll bump a case .005 to .007" in a heartbeat. I've done it for years with no ill effects and better than average accuracy out of my stuff but I'm told it is hard on the brass and can lead to other problems (so can Bourbon). Anyway, now I try to keep the bump at .002" and that seems to work great.

Sometimes, the problem can be brass-specific too (or related to the lack of annealing). In a recent situation with Hornady brass, I had some new stuff that would not chamber after resizing, even with a healthy cam-over. It simply would not bump the shoulder enough for me to cam the bolt shut. I explained this to reloading "expert" and he told me I had a tight chamber. I slapped him across the face for getting fresh and left his establishment, taking my business elsewhere.
 

Seabeeken

Well-Known Member
Joined
Apr 30, 2013
Messages
75
Location
Communist state of maryland
Only ever had 2 die issues. An RCBS 338RCM over sizing the neck and collapsing shoulder and they sent me a new die overnight.
Recently, A redding 250AI die inducing .010 runout. Redding corrected the die and returned it and it has about .001" now.
 

swampbug

Active Member
Joined
Oct 26, 2020
Messages
31
Location
Dallas
You need to have 3-5 reloads before shoulder bumping to allow brass to expand to your chamber. Rely on how hard it is to chamber a round. When you set your die, .002 is generally enough. I like to remove firing pin, and bump back shoulder until bolt just starts to drop (similar to finding seating depth).
 

Primary

LRH Assistant
Here are some related products that LRH members are talking about. Clicking on a product will take you to LRH’s partner, Primary, where you can find links to LRH discussions about these products.

 
 
Top